U.S. patent application number 14/435557 was filed with the patent office on 2015-09-24 for method and device for producing three-dimensional models with a temperature-controllable print head.
This patent application is currently assigned to Voxeljet AG. The applicant listed for this patent is VOXELJET AG. Invention is credited to Ingo Ederer, Daniel Gunther.
Application Number | 20150266238 14/435557 |
Document ID | / |
Family ID | 50383281 |
Filed Date | 2015-09-24 |
United States Patent
Application |
20150266238 |
Kind Code |
A1 |
Ederer; Ingo ; et
al. |
September 24, 2015 |
METHOD AND DEVICE FOR PRODUCING THREE-DIMENSIONAL MODELS WITH A
TEMPERATURE-CONTROLLABLE PRINT HEAD
Abstract
The present invention relates to a method for producing
three-dimensional models by a layering technique, particulate build
material being applied to a build space, and binder material
subsequently being selectively applied to the build material with
the aid of a printer, the binder material containing a moderating
agent and subsequently being sintered with the aid of a heat lamp,
the print head being protected against overheating by active and/or
passive cooling.
Inventors: |
Ederer; Ingo; (Geltendorf,
DE) ; Gunther; Daniel; (Munchen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOXELJET AG |
Friedberg |
|
DE |
|
|
Assignee: |
Voxeljet AG
Friedberg
DE
|
Family ID: |
50383281 |
Appl. No.: |
14/435557 |
Filed: |
October 10, 2013 |
PCT Filed: |
October 10, 2013 |
PCT NO: |
PCT/DE2013/000588 |
371 Date: |
April 14, 2015 |
Current U.S.
Class: |
264/460 ;
425/143; 425/174; 425/174.4 |
Current CPC
Class: |
B29C 64/153 20170801;
B29C 64/165 20170801; B33Y 30/00 20141201; B29K 2105/0005 20130101;
B29C 67/0077 20130101; B29K 2105/251 20130101; B33Y 10/00 20141201;
B29K 2077/00 20130101; B29C 64/364 20170801; B29C 64/386 20170801;
B33Y 50/02 20141201 |
International
Class: |
B29C 67/00 20060101
B29C067/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2012 |
DE |
20 2012 009 796.2 |
Mar 22, 2013 |
DE |
10 2013 004 940.7 |
Claims
1. A device for producing three-dimensional models by a layering
technique, particulate build material being applied to a build
space, a moderating agent subsequently being selectively applied
with the aid of an ink-jet print head, and the printed areas being
solidified by supplying energy, characterized in that the print
head is protected against overheating by active and/or passive
cooling.
2. The device according to claim 1, characterized in that the print
head has a temperature sensor, a temperature controller and
internal means for cooling and for heating.
3. The device according to claim 1, characterized in that the
cooling takes place with the aid of the print medium to be printed;
or the cooling takes place with the aid of cooling air which is
flushed around sensitive parts in the interior of the print head;
or the cooling of the print head takes place by dissipating heat
with the aid of an additional fluid medium; or the cooling takes
place with the aid of Peltier elements.
4. The device according to claim 1, characterized in that the print
head is protected against the residual energy of the build space
and the particulate material and active energy supply on the build
space by partitioning.
5. The device according to claim 1, characterized in that the print
head is protected by an external cooling means.
6. The device according to claim 1, characterized in that the
condensate formation on the print head is prevented by temperature
control and by controlling the humidity.
7. The device for producing three-dimensional models by a layering
technique, particulate build material being applied to a build
space, a moderating agent subsequently being selectively applied to
the build material by a printer, and the printed areas being
solidified by supplying energy, characterized in that a lamp is
used to supply energy, which emits an essentially linearly
distributed radiation and which is guided over the build space in
such a way that the radiation essentially evenly covers the entire
build space.
8. The device according to claims 7, characterized in that the
power of the lamp is controlled in segments and may thus also be
regulated.
9. The device according to claim 3, wherein an evaporator is
disposed in the print head.
10. The device according to claim 4, wherein the device is
characterized by one or any combination of the following: i) the
print head is moved behind a flexible or fixed wall in the build
space; or ii) a collision with the wall is detected by sensors in
the print head or the wall; or iii) the partitioning takes place
using a movable wall; or iv) an air curtain partitions off the
print head.
11. The device according to claim 5, wherein the external cooling
means includes: actively moving cooling air to flow around the
print head; or the print head is brought into contact with a cool
object or a fluid from the outside; or the print head is passively
cooled in a cooled chamber.
12. The device according to claim 6, wherein the device includes
metal cooling plates positioned at reversing points in the build
space for cooling the print head by passing the print head over the
metal cooling plates.
13. The device according to claim 8, wherein the lamp essentially
emits IR radiation in the wavelength range of 1 .mu.m to 4
.mu.m.
14. The device according to claim 13, wherein the lamp is spatially
located at a distance from the print head in its idle position.
15. The device according to claim 14, wherein the lamp is separated
from the print head by partitioning in its idle position.
16. The device of according to claim 15, wherein the partitioning
takes place with the aid of a flexible or fixed wall; or the
partitioning takes place with the aid of an air curtain; or the
partitioning takes place with the aid of a movable wall.
17. The device according to claim 1, wherein the print head has a
temperature sensor, a temperature controller and internal means for
cooling; the cooling of the print head takes place with the aid of
i) the print medium to be printed; or ii) cooling air which is
flushed around sensitive parts in the interior of the print head;
or iii) an additional fluid medium for dissipating heat; or iv)
Peltier elements; and the print head is protected against the
residual energy of the build space and the particulate material and
active energy supply on the build space by partitioning.
18. A method for building a three-dimensional model by a layering
technique comprising: applying a particulate material to a build
space, subsequently selectively applying a moderating agent with an
ink-jet print head for preparing a printed area, supplying energy
to the build space for solidifying the printed area, and protecting
the print head against overheating.
19. The method of claim 18, wherein the step of protecting the
print head includes actively cooling the print head.
20. The method of claim 18, wherein the step of protecting the
print head includes passively cooling the print head.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method and a device for producing
three-dimensional models according to the definition of the species
in Patent Claim 1.
BACKGROUND OF THE INVENTION
[0002] A method for producing three-dimensional objects from
computer data is described in the European patent specification EP
0 431 924 131. In this method, a particulate material is deposited
in a thin layer onto a platform, and a binder material is
selectively printed on the particulate material, using a print
head. The particle area onto which the binder is printed sticks
together and solidifies under the influence of the binder and, if
necessary, an additional hardener. The platform is then lowered by
a distance of one layer thickness into a build cylinder and
provided with a new layer of particulate material, which is also
printed as described above. These steps are repeated until a
certain, desired height of the object is achieved. A
three-dimensional object is thereby produced from the printed and
solidified areas.
[0003] After it is completed, this object produced from solidified
particulate material is embedded in loose particulate material and
is subsequently removed therefrom. This is done, for example, using
an extractor. This leaves the desired objects, from which the
remaining power is removed, for example by brushing.
[0004] Other powder-supported rapid prototyping processes work in a
similar manner, for example selective laser sintering or electron
beam sintering, in which a loose particulate material is also
deposited in layers and selectively solidified with the aid of a
controlled physical radiation source.
[0005] All these methods are referred to collectively below as
"three-dimensional printing methods" or 3D printing methods.
[0006] Of all the layering techniques, 3D printing based on
powdered materials and the supply of liquid binder is the fastest
method.
[0007] Different particulate materials, including polymer
materials, may be processed using these methods. However, the
disadvantage here is that the particulate material feedstock may
not exceed a certain powder density, which is usually 60% of the
density of the solid.
[0008] Nevertheless, the strength of the desired components depends
to a significant extent on the density reached. For a high strength
of the components, it would therefore be necessary to add 40% and
more of the particulate material volume in the form of the liquid
binder. This is a relatively time-consuming process, not only due
to the single-drop supply, but also due to many process problems
which arise, for example, from the inevitable reduction of the
amount of liquid during solidification.
[0009] In another embodiment, which is known to those skilled in
the art as "high-speed sintering," abbreviated as HSS, the
particulate material is solidified by supplying infrared radiation.
The particulate material is physically bound using a melting
operation. The comparatively poor absorption of thermal radiation
in colorless plastics is utilized here. However, this absorption
may be increased many times by introducing an IR acceptor, also
known as a moderating agent, into the plastic. The IR radiation may
be introduced in different ways, e.g., using a rod-shaped IR lamp,
which is moved evenly over the build space. The selectivity is
achieved by printing the particular layer with an IR acceptor in a
targeted manner. The IR radiation is coupled into the particle
material in the areas that are printed much more effectively than
into the unprinted areas. This results in a selective heating in
the layer beyond the melting point and thus to selective
solidification. This process is described, for example, in
EP1740367B1 and EP1648686B1. In these publications, a simple device
is also demonstrated, which, however, is operational only on a
small scale and is not suitable for printing larger build spaces,
since it lacks a corresponding temperature management system.
[0010] The object of the present invention is thus to provide a
scalable device, with the aid of which the HSS process is
facilitated or which at least improves the disadvantages of the
prior art.
[0011] The device according to the invention comprises a build
plane, onto which the layers of the particulate material are
deposited. The build plane is moved layer by layer through a build
space, using a linear positioning unit. The build space may be
defined, for example, by a job box, which may be removed from the
device at the end of the process. The device parts for applying the
layers move within a process chamber. The device for applying the
layer may be, for example, a vibration coater (DE10216013B4) or a
counter-driven roller (EP0538244B1) or a simple scraper, which
applies the particulate material to the build space in a thin layer
that is 20 .mu.m to 300 .mu.m thick, preferably 50 .mu.m to 200
.mu.m thick.
[0012] A print head, which has at least one nozzle end prints the
particular layer with an IR acceptor, is also situated in the
process chamber.
[0013] in principle, it is possible to deposit the IR acceptor in a
vector-like manner onto the build space in the form of a jet or in
the form of single drops. To achieve a suitable resolution, the jet
or drop size should be in a range from 20 to 200 .mu.m. To achieve
higher process speeds, it is advantageous to use a print head which
generates single drops with the aid of a large number of nozzles
and moves over the build plane in a grid-like pattern. An IR lamp,
which illuminates the build plane as a whole or parts of the build
plane in the form of a spot or a line, is also situated in the
process chamber. In the latter two cases, the IR lamp must be moved
over the build space with the aid of a positioning unit in order to
illuminate the entire build space. A rod-shaped IR lamp has proven
to be advantageous, which extends over the entire width of the
build space and lights up a relatively narrow area in the
positioning direction. The positioning units for moving the coater,
the print head and the IR lamp may be designed independently of
each other or in combination. The lamp embodied in the shape of a
rod is advantageously situated on the back side of the coater unit.
In this manner, the coater may carry out the exposure to light when
returning to the starting position, while the movement in the other
direction is used for coating, possibly with reduced lamp power.
The print head in this embodiment may be mounted on another moving
axis farther behind [sic; the] lamp.
[0014] The build plane preferably moves in a build cylinder which
is open at least on the side of the build plane and forms the build
space together therewith. The build space may advantageously be
removed from the device at the end of the printing process. The
device may then carry out a new layering process by inserting
another build space.
[0015] The HSS process may be used to process many polymer
materials in particulate form, for example polyamide. Graphite, for
example, may be used as the IR acceptor, which is mixed in a
carrier fluid in the form of a suspension. Various easy-to-print
fluids, such as isopropyl alcohol, din/ethyl succinate and, with
restrictions, ethyl alcohol or water, are suitable as carrier
fluids.
[0016] The process must be set in such a way that the temperature
in the printed areas is above the melting point of the particulate
material, at least for a short period of time. In the case of
polyamide 12, or PA 12 for short, this temperature is approximately
180.degree. C. On the other hand, the temperature in the unprinted
areas should be as low as possible, since the polymer material may
change irreversibly even at lower temperatures.
[0017] The quantity of IR energy introduced into the particulate
material may be set, for example, by means of the lamp power or by
means of the speed at which the rod-shaped lamp moves over the
build space. The disadvantage of the method is that the carrier
fluid for the IR acceptor evaporates in the printed areas and,
during this process, the temperature thereby decreases in the
areas. It is therefore advantageous to increase the temperature in
the build space to a higher level with the aid of suitable measures
in order to minimize the necessary temperature difference that must
be overcome with the aid of the lamp. Care should also be taken to
avoid selecting too high a temperature in order to minimize damage
to the particulate material. In principle, it is also possible to
preheat the particulate material prior to coating. However, it has
been demonstrated that the particulate material very quickly adapts
to the ambient temperature during and after coating and dissipates
the thermal energy again. A temperature range of 60.degree.
C.-120.degree. C. for PA 12 has been demonstrated to be
advantageous for a build space atmosphere. A temperature range of
75.degree. C. to 95.degree. C. is even more advantageous. It is
possible that the particulate material would already begin to react
with the oxygen in the air at these temperatures. It may therefore
be necessary to apply a protective gas to the build space.
Nitrogen, for example, is suitable as the protective gas; other
gases such as argon may also be used.
[0018] To increase the temperature in the build space to the
desired level, it may be necessary to provide additional heating
means in the device. This may be done, for example, in the form of
IR radiators above the build space, which heat the entire build
space as evenly as possible. However, it would also be conceivable
to remove the air from the process chamber, heat it using
corresponding means, such as a heater battery, and blow it back
into the process chamber in a targeted manner. Moreover, it is
advantageous if the heat in the process chamber is maintained at a
preferably constant level. For this purpose, a temperature
controller is advantageous, which regulates the heating means in
the build space in interaction with a temperature sensor. The
temperature gradient on the build space should not exceed
10.degree. C. To simplify the temperature regulation, it is
desirable if as little heat as possible is lost to the
surroundings. It is therefore necessary to insulate the process
chamber using suitable measures and to provide corresponding seals
on doors and flaps. The same applies to the build space, which is
also designed in such a way that little heat is dissipated to the
surroundings. This is done by providing the build cylinder with a
double-walled design, including corresponding insulation at the
contact points. In principle, it is also possible to compensate for
the temperature loss in the build space by means of an active
heating, e.g., of the inner walls of the build cylinder and/or the
building platform. Another option is to actively introduce
preheated gas into the build space, which acts as an energy carrier
and transfers the heat to the particulate material feedstock. The
gas may be introduced, for example, by means of bores in the
building platform.
[0019] So-called filament dispensers, which deflect a fluid stream
onto the build space via a nozzle, may be used as the print head.
The fluid stream contains the IR acceptor, e.g., in the form of
solid graphite particles in a solvent suspension. The nozzle should
have a diameter of 0.1-0.5 mm for a suitable print resolution. A
valve may be inserted upstream from the nozzle, which is able to
quickly switch the fluid stream. The nozzle should be moved over
the build space at a short distance of only a few mm to ensure the
positioning accuracy of the deposition of the fluid stream. The
filament dispenser is moved over the build space in a vector-like
manner with the aid of at least two linear axes. The kinematics
preferably comprise a portal with three linear axes. In principle,
other kinematics of motion are also conceivable, for example, an
articulated arm robot, which guides the filament dispenser over the
build space.
[0020] In one preferred embodiment, the IR acceptor is dispensed in
fluid form onto the build space using a print head which includes a
large number of single-drop generators. Print heads of this type
are known from many applications, including 3D printing, where a
binder instead of the IR acceptor is dispensed in layers onto a
particulate material.
[0021] Drop generators of this type work according to different
principles, for example the piezo principle or the bubblejet
principle. In addition to these so-called drop-on-demand single
drop generators, continuous systems are also known, in which a
switchable stream of single drops is generated. In principle, all
these systems are suitable for the aforementioned task; however,
the piezo systems have significant advantages with regard to
lifespan, performance and economic feasibility.
[0022] Piezoelectric printing systems work with one or multiple
open nozzles. The nozzle diameters are usually less than 80 .mu.m.
A pressure pulse is briefly applied to the fluid in equally small
pump chambers with the aid of a piezoelectric actuator. The fluid
is significantly accelerated in the nozzles and emerges therefrom
in the form of drops. Due to this functionality, certain limits are
imposed on the present device. Thus, the fluid must have a
relatively low viscosity. The viscosity should preferably be less
than 20 mPas. In addition, the IR acceptor particles mixed into the
carrier fluid must be much smaller than the narrowest channel width
in the printing system. As a result, the particles are preferably
smaller than 5 pm and even more preferably smaller than 1 .mu.m.
Due to the operating principle of the printing system using the
pressure surge, it is necessary for all channels and the pump
chambers to be filled with the fluid without any gas bubbles. To
maintain this condition during operation as well, it is necessary
either to select a carrier fluid which has an evaporation
temperature above the operating temperature or to control the
temperature of the fluid in such a way that no phase transition of
the fluid takes place. Moreover, the piezoelectric actuators have a
limit temperature up to which they usually may be heated without
sustaining irreversible damage. This temperature is usually under
120.degree. C.
[0023] It is apparent from the above discussion that the printing
system must be protected against excessive IR radiation in the
process chamber, on the one hand, and the temperature of the
printing system must be regulated independently with respect to the
process chamber temperature, on the other hand.
[0024] The printing system may be protected against the IR
radiation by means of corresponding shielding and/or by the
distance to the radiation sources. This may be effectively
accomplished with radiation sources from above and from the sides.
However, it is difficult to protect the print head against
radiation from below, since it must move at a very short distance
of 1-5 mm, preferably 2-3 mm from the powder bed. This short
distance is necessary to ensure a precise positioning of the small
fluid droplets on the build space. For this reason, it is necessary
to keep the dwell time of the print head over the hot build space
as short as possible.
[0025] Despite the aforementioned measures, the desired temperature
of the printing system, which is 40.degree. C.-60.degree. C., is
much lower than the temperature of the process chamber.
Corresponding cooling measures must be provided therefor.
[0026] These measures are divided into internal cooling, external
cooling and partitioning. Only a combination of different measures
facilitates a precise regulation. Regulating the temperature is
necessary, since the viscosity of the print fluid is greatly
dependent on the temperature. The dispensing capacity of the print
head, in turn, is linked to the viscosity. Consequently, an
imprecise regulation may result in fluctuating supply of the
moderating agent.
[0027] This may result in component distortion. For the purpose of
more detailed explanation, the invention is described in greater
detail below on the basis of preferred exemplary embodiments with
reference to the drawing.
[0028] In the drawing:
[0029] FIG. 1 shows a method known from the prior art.
[0030] FIG. 2 shows a diagram of the process sequence of a 3D
printer which operates according to the HSS principle;
[0031] FIG. 3 shows a graphic representation of the dwell times of
the print head above the heated build space in a process according
to FIG. 2;
[0032] FIG. 4 shows a representation of the structure of the print
head according o the prior art;
[0033] FIG. 5 shows a diagram of the control of the temperature of
a print head according to the prior art;
[0034] FIG. 6 shows an expanded diagram of the control of the
temperature of a print head according to the prior art, including
internal or external print head cooling;
[0035] FIG. 7 shows a diagram of the cooling process by means of
flushing or nozzle actuation;
[0036] FIG. 8 shows an isometric view and a side view of a print
module, with an indication of the flaw lines of the cooling
air,
[0037] FIG. 9 shows a sectional view of the coolant channels for
cooling the modules and the cover plate;
[0038] FIG. 10 shows a sectional view of the Peltier elements for
actively cooling the print head with the aid of massive cooling
lines;
[0039] FIG. 11 shows a sectional view of a print head, including
surfaces for cooling through evaporation;
[0040] FIG. 12 shows a top view of a preferred device having
partitioning in a block diagram;
[0041] FIG. 13 shows side view one preferred embodiment, including
a partition wall;
[0042] FIG. 14 shows a top view of one preferred embodiment,
including different partitioning means;
[0043] FIG. 15 shows a side view of one preferred embodiment,
including an air curtain;
[0044] FIG. 16 shows a side view of one preferred embodiment,
including a print head air cooling means;
[0045] FIG. 17 shows a side view of a device for active contacting
with a fluid-cooled cleaning device and a cooling block;
[0046] FIG. 18 shows a top view of a device according to the
invention, including cooled build space edges;
[0047] FIG. 19 shows a top view of one preferred embodiment,
including a linear lamp, segmented activation and a diagram for the
movement speed.
[0048] FIG. 1 shows a known device according to the prior art. It
is used to produce bodies such as object 103. Body 103 may have a
nearly arbitrary complexity. The device is referred to below as a
3D printer.
[0049] The process of constructing a body 103 begins in that
movable building platform 102 is moved to its highest position in
device 104. At least one layer thickness is also present between
building platform 102 and the lower edge of coater 101. The coater
is moved to a position in front of build space 111 with the aid of
an axis system, which is not illustrated. In this position, coater
101, including its stock 113 of particulate material, is caused to
vibrate. The particulate material flows out of gap 112. Outflowing
material 110 fills the still empty layer due to a forward movement
106 of coater 101.
[0050] Subsequently or even during the movement of coater 101,
print head 100 is set in motion by an axis system, which is also
not illustrated. The latter follows a meandering path 105, which
passes over the build space. According to the sectional diagrams of
body 103 to be produced. the print head dispenses drops of binder
109 and solidifies these areas. This basic principle remains the
same regardless of print head 100 used. Depending on the size, in
extreme cases, meandering path 105 is reduced to a simple forward
and backward movement,
[0051] After printing, building platform 102 is moved in direction
108. A new layer 107 for coater 101 is generated thereby. The layer
cycle begins all over again when coater 101 returns to its starting
position. Repeatedly carrying out this cycle produces component
[sic; body] 103 in the end. After the building process. component
[sic: body] 103 may be removed from the loose powder still
surrounding it.
[0052] The solidification process described above, in which the
particles of the particulate material are sintered, is one variant
of this process. FIG. 2 shows the sequence of a method of this
type. It is an expansion of the 3D printer described above.
[0053] The representation under I shows the printing process, which
takes place in a manner similar to the above description. Print
head 100 undergoes a meandering movement and deposits drops,
including moderating agent 109. in the area of component [sic:
body] 103. In terms of many of its parts, device 104 is structured
like a 3D printer. The drop generation is preferably based on the
piezoelectric principle, since print heads having maximum lifespans
may be built hereby. This effect may be used only up to a certain
limit temperature TLimit. Above this temperature, the drop
generation is disturbed, or the drop generator sustains
irreversible damage.
[0054] Step II deviates from the above description. A heat lamp,
which generates radiation 201 adapted to the moderating agent, is
guided over the build space. When it reaches the printed sites, the
heat is effectively coupled into the particulate material and
causes it to be sintered. The rest of the build space also absorbs
not inconsiderable amounts of heat.
[0055] Process steps III and IV are again entirely similar to the
description of 3D printing. Building platform 102 is first lowered
into device 104 in direction 108. Coater 101 then fills layer 110
with new particulate material.
[0056] FIG. 3 shows a top view of a preferred device according to
the invention. Print head 100 is omitted for the purpose of better
illustrating meandering print head path 105. It is apparent that
the print head executes large sections of its movement over build
space 111. Simplified, the build space has a fixed temperature
T111. At the beginning of the process, the print head has
temperature T100=TBegin. FIG. 3 also shows a schematic
representation of the dwell time of print head 100 over build space
111. The diagram shows the process steps from FIG. 2.
[0057] Assuming that the build space has temperature T111, the
following conditions arise, which are illustrated in the other
diagrams in FIG. 3. The print head heats up over the build space.
Afterwards, it may again transfer heat to the surroundings in its
idle position. Depending on the heat absorption over the build
space and the heat dissipation in the idle position, a stationary
temperature between start temperature TStart and build space
temperature T111 sets in. It is demonstrated that, if a higher
printing capacity is desired, the print head must be protected
against overheating above TLimit with the aid of active and/or
passive cooling. To ensure uniform dispensing capacities, the print
head must also be maintained within a very narrow temperature
range. Temperatures of 40-60.degree. C. are particularly preferred
in this case. According to experience, a control of .+-.2.degree.
C. delivers good print results.
[0058] FIG. 4 shows the structure of a print head 100 according to
the prior art. Various assemblies are integrated into housing 212.
Print modules 400 are essential for drop generation 109. These
print modules contain the nozzles, the piezoelectric drives and the
fluid system for distributing the fluid. A heater is usually also
integrated for temperature regulation. These modules 400 are
frequently purchased from print head manufacturers such as Dimatix,
Xaar, Seico, Epson, Konica or Kyocera. Intervention into the inner
structure is not possible. Modules 400 are connected to a storage
tank 401, which contains print fluid 408, by hoses, a valve 406 and
a filter 407. Electrical connections exist to heating controller
413 and data electronics 414. The connections are run to the
outside (415, 416). The storage tank is connected to underpressure,
overpressure and the refill line by additional lines switched by
valves (409, 410 and 411). These lines are again run to the outside
(417, 418 and 419).
[0059] On the underside, the print head is protected against the
penetration of fluids or contaminants by a cover plate 402. The
modules and the cover plate absorb heat 404 in the form of
radiation and convection during the travel over build space 111. If
the temperature exceeds the setpoint of the heating controller, the
temperature may no longer be held at a constant level.
[0060] FIG. 5 shows the heating controller of existing print heads
as a block diagram. Heating system 501 itself is controlled by a
power controller 503. It receives its control signals from a
controller 504, which, together with a sensor 500, detects the
temperature directly in module 400 and thus implements a closed
control circuit. The heat losses due to heat conduction to the
surrounding parts, the convection in the housing and the thermal
radiation losses are identified by 502. Energy is also transferred
along with heated fluid drops 109 if the temperature of the drops
is higher than the temperature of the refilled fluid. All losses
must be compensated for by the heating system. The temperature at
the lower end of the module is relevant for drop formation.
[0061] FIG. 6 shows the design of a print head according to the
invention. A massive heat flow 404 is added to the aforementioned
variables in this case. In the HSS process described above, this
heat flow is greater than the dissipated amounts of heat. The
control by the print head-internal heating system may be
facilitated only by introducing additional cooling 600. Cooling
system 600 may include all preferred embodiments according to the
invention.
[0062] The form of heat dissipation illustrated in FIG. 7 is also
covered by 600. In principle, two options exist. On the one hand,
cold print fluid may be pressed through the print head. For this
purpose, an overpressure 700 is applied to module 400 or to storage
tank 401 (FIG. 4). A large amount of fluid is dispensed, and colder
fluid enters module 400. In one preferred embodiment of the
invention, the fluid enters print head 100 or print module 400 from
a reservoir outside the build space at room temperature via
insulated lines. This form of cooling may likewise take place via
the drop generator of the print head. As in standard operation, an
overpressure 702 is present at the tank.
[0063] The intensity of this form of cooling must be ascertained by
controller 504 of print head heating system 501. If the temperature
leaves the control range in the upward direction, more intensive
cooling is required. This scenario may be detected by the switching
times of heating system 501.
[0064] The cooling of module 400 may also be achieved via its
housing. For this purpose, compressed air 800 may flow to the
housing to compensate for heat absorption 404 from below. The
compressed air nozzles may also be disposed in such a way that the
flow rises vertically on the print module. In both embodiments of
the invention, cover plate 402 (FIG. 4) must seal the modules
toward the build space so that no particulate material is swirled
up.
[0065] FIG. 9 shows another preferred embodiment of the invention.
In this case, heat 404 to be dissipated is transferred from module
400 to a fluid by heat conduction. For this purpose, contact blocks
900 on module 400 and cover plate 402 are disposed in a way that
facilitates good heat transfer. Contact blocks 900 have bores 903,
in which cooling fluid 901 may flow. Connections 902 connect the
contact blocks to a hose system, which passes out of the print head
and the warm build space. The hose system has an insulated design.
Depending on the accumulating heat, cooling fluid 901 is then
cooled passively or actively.
[0066] FIG. 10 shows a likewise preferred device. In this case,
excess heat 404 at module 400 is also dissipated via contact blocks
1000. In this case, the latter are in contact with Peltier elements
1002 via massive copper connections 1001. The Peltier elements pump
the heat out of print head housing 412 when a voltage is applied to
contacts 1004.
[0067] The evaporation of a liquid may also be used for cooling.
FIG. 11 shows an arrangement of this type. Heat 404 at module 400
is dissipated to cover plate 402 by heat conduction. A fluid 1102,
which has a suitable evaporation point, is continuously redispensed
thereto. The energy is taken from steam 1100 and guided out of the
print head using a discharge system 1101 to avoid harmful
condensation. For example, if water is selected as the fluid,
temperatures around 100.degree. C. may be controlled.
[0068] FIG. 12 shows one preferred embodiment in the form of a
block diagram. Print head 100 is separated from the build space by
a partition 1200. In the phase of sintering, lowering and coating
(FIG. 3, II, III, IV), print head 100 may thus cool without
absorbing any more radiation from build space 111. The convection
is also reduced. In the same manner, another partition 1201 may
ensure that no additional heat reaches print head 100 due to the
still warm lamp 200 during the passage of print head 105.
[0069] FIG. 13 shows a side view of one preferred embodiment of the
invention. Partition 1300 for print head 100 is rotatably
supported. Print head 100 may thus strike the partition and reach
build space 111. An energy exchange takes place only when it passes
through. Partition 1300 forms a chamber for the print head in which
it may cool. Likewise, partition 1301 may be designed for coater
101 and lamp 200.
[0070] The partitions illustrated in FIG. 13 may also be designed
to be active, as shown in FIG. 14. Once again, one partition 1400
may be provided for print head 100, and one partition 1401 may be
provided for coater 101 and lamp 200. Compared to the rotatably
supported partition, this has the advantage of lesser restrictions
in the movement of the units in build space 111. The opening times
may also be designed to be very short, For example, pneumatic
actuators or electrically driven spindles are suitable as
drives.
[0071] FIG. 15 shows one preferred embodiment of the partitioning
means. Moving parts are dispensed with, Nozzles 1501, 1500, 1502
allow air having different temperatures to flow in the direction of
build space 111 as a curtain. If a laminar flow is set, only a
limited mixing of the air masses 1503, 1505 and 1504 takes piece.
The temperature may be controlled and also regulated in segments
via corresponding heating and cooling units.
[0072] According to the invention, it is not only possible to cool
print head 100 by partitioning or from the inside, but the print
head may also be cooled from the outside. FIG. 16 shows a design of
this type. Print head 100 is flushed with cooling air 1601 and
1603. This air is discharged from nozzles 1600 and 1602. The flow
of cooling air should not interact with the particulate material.
It is therefore particularly preferred to combine the cooling with
a partitioning.
[0073] FIG. 17 shows another means of cooling the print head from
the outside. Print head 100 is brought directly into contact with a
heat-dissipating material. This may be a fluid which absorbs the
heat. This may be combined with a cleaning device for the print
head. A counter-rotating roller 1700 may be brought into contact
with print head 100 moving in direction 105. The roller, which has
been moistened by a shower 1702 or a fluid-filled basin 1703,
absorbs heat from the print head. A good thermally conductive body
1701 may also be pressed onto cover plate 102 of print head 100.
This body, in turn, is passively or actively cooled, for example
using a cooling fluid 1704.
[0074] Print head 100 may cool not only in its idle position but
also on its path 105 on the edge of build space 111. For this
purpose, build space edges 1800 must be colder than the build
space. This may be achieved by the fact that edges 1800 of build
space 111 are designed as pipes through which cooling air 1801
flows.
[0075] FIGS. 19 and 20 show of one particularly preferred
embodiment of the invention FIG. 19 shows the design of lamp 200 in
an essentially linear embodiment. A homogeneous illumination of
build space 111 is achieved. Due to the control, the direct
influence of the print head may be minimized. Since cooler areas
may occur on the edge of the build space, despite a uniform
radiation power, due to the air circulation, additional segments
2000 may be mounted here, or a lamp with segmented control of the
power may be used.
[0076] FIG. 19 also shows a diagram for a particularly preferred
control of the lamp movement of a linearly designed lamp. Due to
the convection on build space 111, it is sensible to irradiate the
edges at a slower movement speed while maintaining a constant
power. It is likewise possible to adjust the power. The inertia of
the lamp imposes limits on the method.
LIST OF REFERENCE NUMERALS
[0077] 100 Print head [0078] 101 Coater [0079] 102 Building
platform [0080] 103 Body [0081] 104 Device [0082] 105 Print head
path [0083] 106 Coater path [0084] 107 Built layers [0085] 108
Direction of building platform [0086] 109 Microdrops [0087] 110
Particulate material roll [0088] 111 Build space [0089] 112 Coater
gap [0090] 113 Powder stock [0091] 200 Heat lamp [0092] 400 Print
module [0093] 401 Storage tank [0094] 402 Cover plate [0095] 403
Heated surface [0096] 404 Heat transfer [0097] 406 Valve [0098] 407
Filter [0099] 408 Printing fluid [0100] 409 Valve for underpressure
[0101] 410 Valve for overpressure [0102] 411 Valve for refilling
[0103] 412 Print head housing [0104] 413 Heating controller [0105]
414 Data electronics [0106] 415 Feed-through for data electronics
[0107] 416 Feed-through for heating controller [0108] 417
Feed-through for underpressure line [0109] 418 Feed-through for
overpressure line [0110] 419 Feed-through for refilling line [0111]
500 Temperature sensor [0112] 501 Heating [0113] 502 Heat
dissipation [0114] 503 Power controller [0115] 504 Controller
[0116] 600 Cooling [0117] 700 Overpressure [0118] 701 Overpressure
jet [0119] 702 Underpressure [0120] 800 Flow, horizontal [0121] 801
Flow, vertical [0122] 802 Air nozzles [0123] 900 Contact block
[0124] 901 Cooling fluid [0125] 902 Cooling line* [0126] 903
Cooling pipe [0127] 1000 Contact block [0128] 1001 Massive heat
conductors [0129] 1002 Peltier element [0130] 1003 Pumped-off heat
[0131] 1004 Electrical contacting [0132] 1100 Steam [0133] 1102
Fluid [0134] 1101 Steam guidance [0135] 1200 Print head partition
[0136] 1201 Coater partition [0137] 1300 Rotatable print head
partition [0138] 1301 Rotatable coater partition [0139] 1400
Movable print head partition [0140] 1401 Movable coater partition
[0141] 1500 Air nozzles for build space flow [0142] 1501 Air nozzle
for print head flow [0143] 1502 Air nozzle for coater flow [0144]
1503 Print head flow [0145] 1504 Coater flow [0146] 1505 Build
space flow [0147] 1800 Build space edge [0148] 1801 Cooling air for
build space edge [0149] 2000 Additional lamps
* * * * *